Conventionally, a drive assist technique for vehicle, which displays a peripheral vehicle or notifies an approach of the peripheral vehicle using alarm, is known. Herein, the display or the alarm is activated based on information indicating detection of the peripheral vehicle that may exist in front of a subject vehicle. For example, Patent Literature 1 describes a technique that displays a front vehicle detected by a sensor, such as a camera or a radar. Hereinafter, the sensor, such as the camera or the radar will be referred to as a vehicle detection sensor.